Pressure-sensitive recording paper

ABSTRACT

A pressure-sensitive recording paper comprising a layer of microcapsules containing a color former and a layer of a color developer, said layers coated on the same support or different supports, and at least one of said layers containing an ether derivative of an aromatic hydroxyl compound.

Matted States Patent Ishige et al.

[ Oct. 30, 1973 PRESSURE-SENSITIVE RECORDING PAPER Inventors: Sadao Ishige; Takao Hayashi;

Hiroharu Matsukawa, all of Ashigara-Kamigun, Kanagawa, Japan Fuji Photo Film Co., Ltd., Kanagawa, Japan Filed: July 8, 1971 Appl. No.: 160,775

Assignee:

Foreign Application Priority Data July 8, 1970 Japan 45/59698 US. Cl. 117/361, 117/368, 117/155 L,

260/38, 260/415 R Int. Cl. 841m 5/22 Field of Search 117/362, 36.8, 36.9

[56] References Cited UNITED STATES PATENTS 3,455,721 7/1969 Phillips et a1. .i 117/361 3,509,174 4/1970 Lin 117/362 3,592,677 7/1971 Tsuboi et al. 117/362 Primary Examiner-Murray Katz Attorney-Richard C. Sughrue et al.

[57] ABSTRACT 6 Claims, 6 Drawing Figures DENSITY (D) DENSITY PATENTEBBCT 30 I973 SHEET 2 BF 4 40 s40 so WAVELENGTH (my) WAVELENGTH (my) DENSITY (D) DENSITY (D) WAVELENGTH (my) WAVELENGTH (m PAIENIEBncI 30 I975 DENSITY DENSITY SHEET 3 DE 4 DENSITY (D) WAVELENGTH 700 WAVELENGTH (my DENSITY (D) I l fi 460 540 620 700 WAVELENGTH (my) WAVELENGTH Imp) PAIENTED "CI 3 0 I973 DENSITY D DENSITY (D I SHEET E 0F 4 WAVELENGTH (my) WAVELENGTH DENSITY (D WAVELENGTH (my) PRESSURE-SENSITIVE RECORDING PAPER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a pressure-sensitive record- 5 2. Description of the Prior Art Pressure-sensitive recording paper, as it has been known, for example, by US Pat. Nos. 2,712,507, 2,730,465, and 2,730,457, is based on the utilization of microcapsules containing a solution of a substantially colorless organic compound (hereinafter, referred to color former) and an electron-accepting adsorbent substance (hereinafter referred to color developer).

In this application, an upper sheet means a support having coated thereon, a layer of microcapsules containing a color former; an intermediate sheet means a support having coated on one surface, a layer of microcapsules containing a color former and having coated on the opposite surface, a layer of color developer; and an undersheet means a support having coated thereon, a color developer. Further, a single-fold sheet means a support having coated thereon, a layer of microcapsules and a color developer, simultaneously.

Illustrative of the color formers are malachite green t n which s ,.3-b (eim MlamimnhsnrD- phthalide, benzoyl leuco methylene blue, crystal violet lactone, which is 3,3bis(p-dimethylaminophenyl)-6 dimethylamino phthalide, Rhodamine B lactam, 3- dialkylaminoJ dialkylamino-fluorans, and 3 -methyl- On the other hand, the color developen which is capable for forming a color dye when contacted with the color former, may be an active clay substance, such as acid clay, active clay, attapulgite, zeolite or bentonite, and organic acidic substances, such as succinic acid, tannic acid, gallic acid, pentachlorophenol and phenol resins.

The light resistance of the color dye formed by reaction of the color former and color developer depends upon the structure of the color former and also upon the color developer. The color developers now in wide use are clays, such as acidic clay. The light resistance of the color dye formed on an under sheet using this developer, although differing in the type of the color former, is generally poor except benzoyl leucomethylene blue. Hence, when such a paper is left indoors or exposed to sunlight, the density of the color dye formed on the paper is easily reduced; that is, the color changes easily. Accordingly, the commercial availability of pressure-sensitive recording paper is reduced.

The color former most often employed is a mixture of crystal violet lactone and benzoyl leuco methylene blue. Since crystal violet lactone has a very poor resistance to light, the color dye formed on the color developer sheet fades when allowed to stand indoors or exposed to sunlight. Consequently, only the light blue color formed from methylene blue remains, which obviously reduces the commercial value of the recording paper. For the production of a black color or green color, m nq:7rdi thyl miwfluq an isusefii It develops a green cdlor on acid clay, but changes to red brown on standing indoors or on exposure to sun. light. Accordingly, the black or green color formed by.

3benzylamino-7-diethylaminofluoran assumes a reddish color on standing indoors or exposure to sunlight, resulting in a reduction in the commercial value of the pressure-sensitive recording paper.

SUMMARY OF THE PRESENT INVENTION It is an object of this invention to provide a pressuresensitive recording paper having excellent resistance to light.

The foregoing object is achieved by incorporating at least one ether derivative of an aromatic hydroxyl compound in the coating layer of the pressure-sensitive recording paper.

DETAILED DESCRIPTION OF THE INVENTION Examples of the ether derivative of the aromatic hydroxyl compound applicable to this invention include p-chloroanisole, p-methylanisole, p-acetoxyanisole, pacetaminoanisole, o-chloroanisole, m-chloroanisole, N

B-cyanoethyl p-anisidene, pqs ktwnmflahwsyhs zqn n n albi(p-methoxyphenyl)propane, catechol dimethyl ether, resorcinol dimethyl ether, hydroquinone dimethyl ether, catechol diethyl ether, resorcinol dipropyl ether, hydroquinone dibutyl ether, p-methoxybenzoic acid ethyl ester, p-ethoxybenzenesulfonamide, l-phenoxy-- 2-cyanoethane, lphenoxy-Z-hydroxyethane, lphenoxy-Z-chloroethane, diphenyl ether, hydroquipounds to a color developer.

The acceptable amount of the ether derivative of the aromatic hydroxyl compound applicable to this invention ranges from 10 to 200% by weight based on the weight of the color former used, or 0.2 to 10% based on the weight of the color developer used.

Microcapsules containing the color former may be produced, for example, by the process disclosed in U.S. Pat. No. 2,700,458, but the process of microcapsulation is not limited to such, since the present invention is directed to incorporation of the ether derivative.

A better understanding of the present invention will be attained from the following examples, which are merely intended to be illustrative and not limitative of 'the present invention. All parts are by weight unless otherwise stated.

Example I former oil in which 3% of hydroquinone dimethyl ether had been dissolved. This mixed solution was emulsified and dispersed. The color former oil consisted of a solution of four parts of diphenyl chloride and one part of kerosene in which 2% of crystal violet lactone was dissolved.

When the average sizes of the oil droplets reached 5 microns, the emulsification was stopped. Water at 40 C. was added to the emulsion to make 900 parts, and stirring was continued. In this case, caution should be taken not to lower the temperature below 40 C. Thereafter, acetic acid was added to adjust the pH of the liquid to 4.0 and thereby induce coacervation. Stirring was further continued for minutes, and then the mixture was cooled with ,ice water to cause gelation of coacervate films deposited around the oil droplets. When the temperature of the liquid became 20 C., seven parts of a 37% formaldehyde solution were added. When the temperature dropped to 10 C., an aqueous 15% solution of sodium hydroxide was added to adjust the pH to 9. The addition of the sodium hydroxide was performed with meticulous care so as not to coagulate the system. With continued stirring, the liquid was heated to 50 C. After cooling to C., the microcapsule liquid thus obtained was coated onto a paper having a unit weight of 40 g/rn in an amount of 6 g/m as solid content, and dried to make an upper sheet of pressure sensitive recording paper.

Example 2 To 40 parts of a color former oil consisting of a solution of 2% crystal violet lactone in an oil conposed of four parts of diphenyl chloride and one part of kerosene was dissolved 3%, based on the color former oil, of N-(B-cyanoethyl) p-anisidine. The solution was microencapsulated in the same manner as in Example 1. The resulting microcapsule liquid was coated onto a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording paper.

Example} I To 40 parts of a color former oil obtained by dissolving 2% crystal violet lactone in an oil consisting of four parts of diphenyl chloride and one part of kerosene was dissolved 3% by weight, based on the oil, of pmethylanisole. The solution was microencapsulated in the same way as in Example l. The res uIting microcapsule liquid was coated o rito a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording paper.

C0MPARATIYE EXAMPLE 1 40 parts of a color former oil obtained by dissolving 2% crystal violet Iactone in an oil consisting of four parts of diphenyl chloride and one part of kerosene was microencapsulated in the same manner as in Example I. The resulting microcapsule liquid yv a s coated onto a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried-to form an upper sheet of pressure-sensitive recording paper.

In order to perform comparative tests on the upper sheets obtained in Examples 1 to 3 and Comparative E ple asun er 1 96! wssa ssius sa w zh Method of production of under sheet.

Eight parts of a 20% sodium hydroxide was added to 300 parts of water, and with stirring, 100 parts of acid clay (product of the Mizusawa Kagaku Kogyo Kabu shiki Kaisha) was gradually added. After thorough stirring, the stirring was made slower, and 20 parts (as solid content) of styrene butadiene rubber latex (Dow 620, tradename manufactured by the Dow Chemical Company) was gradually added to form a coating solution. The coating solution was coated on raw paper having a unit weight of 40 g/m in an amount of 10 g/m as solid content, and dried to form an under sheet of pressure sensitive recording paper for test purposes. Comparative test 1 Each fthssnrs ee Q E mP s d 3 n if Comparative Example 1 was superposed on the under sheet, and a pressure of 600 Kg/cm was applied to produce a color. After allowing the specimen to stand for 1 hour in dark, the spectral absorption curve (fresh) in a wave-length region of 700 to 380 mp. was measured with respect to the developed color. The results are shown in FIG. 1,(1)'to (4)..

The measurement of the spectral absorption curve was performed using a Beckman spectrophotometer, Type DB. The light resistance values were obtained as follows:

density at the absorption maximum after sunlight exposure fresh density at the absorption maximum Light resistance X 100 The results obtained are shown in Table 1 below:

TABLE I.L1GHT RESISTANCE VALUES OF CRYSTAL VIOLET LACTONE AT THE ABSORPTION MAXIMUM AFTER SUNLIGHT EXPOSURE I One hour Three hour sunlight sunlight exposure exposure Numbers of (percent) (percent) Figure Example I. 651 4L3 (I) Example 2. 59.l 32.6 (2) Example 3. 54.2 32.l (3) 46.4 21.6 (4) Comparative Example let Iactone.

Exam? Example 5 In 40 parts of a'color former oil obtained by dissolvl ififii l i j IQPIFPPKPEEZSLQQEKQEPEE! IE3) oil consisting of four parts of diphenyl chloride and one part of kerosene was dissolved 3%, based on the oil, of N-(B-cyano-ethyl)-p-anisidine. The solution wa s microencapsulatedin the same wayas in Example 1. The resulting microcapsule liquid was coated on a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording paper.

Example 6 COMPARATIVE EXAMPLE 2 40 parts of a color former oil obtained by dissolving 2% 3-methyl-2,2'-spirobi(benzo[fjchromenefin an oilconsisting of four parts of diphenyl chloride and one part of kerosene was microencapsulated in the same way as in Example l. The resulting microcapsule solution was coated on a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording paper. Comparative test 2 Each of the upper sheets obtained in Examples 4, 5 and 6 and Comparative Example 2 was superposed on the test under sheet, and a pressure of 600 Kg/cm was applied to develop a color. After allowing the paper to stand for one hour in dark, the spectral absorption curve (fresh) of the developed color in a wavelength region of 700 to 380mg. was measured. The measurement was also made after exposing the specimens to sunlight for 1 hour and 3 hours, respectively. The results are shown in FIG. 2, (l) to (4). The light resistance values were calculated in the same way as in Comparative Test 1. The results are shown in Table 2:

TABLE 2.LlGHT RESISTANCE VALUES OPE- METHYL- 2,2'-SPlR()BI(BENZO[F]CHROMENE) AT THE ABSORP- TION MAXlMUM AFTER SUNLlGHT EXPOSURE One hour Three hour It is seen from the foregoing results thatthe light re sistance of 3-methyl-2,2'-spirobi(benzo[f]chromene) is increased by using the ether derivative of the aromatic hydroxyl compound, and its color changes very little.

Example 7 To 40 parts of a color former oil obtained by dissolv oil consisting of four parts of diphenyl chloride and one part of kerosene was dissolved 3%, based on the oil, of hydroquinone dimethyl ether. The solution was microencapsulated in the same way as set forth in Example 1. The resulting microcapsule liquid was coated on a paper having unit weight of 4Og/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording paper.

Exanipl'e 8 To 40 parts of a color former oil obtained by dissolvin g6?) 3 dibenzylamin0 7-dieTh yla minofluoran in an oil consisting of four parts of diphenyl chloride and one part of kerosene was dissolved 3%, based on the oil, of N-(B-cyanoethyl)p-anisidine. The solution was microencapsulated in the same way as in Example 1. The resulting microcapsule liquid was coated on raw paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording papers.

Eimple 9- To 40 parts of a color former oil obtained by dissolvin the same way as s et forth in Example 1. The resulting microcapsule liquid was coated on a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressuresensitive recording paper.

C OMFAEATI VE EYAWIFEE? 40 parts of a color former oil obtained by dissolving 5% 3-dibenzylamino-7-diethylamintfiluoran in an oil consisting of four parts of diphenyl chloride and one part of kerosene was microencapsulated in the same way as in Example 1. The resulting microcapsule liquid was coated on a paper having a unit weight of 40 g/m in an amount of 6 g/m as solid content, and dried to form an upper sheet of pressure-sensitive recording pa-' per. C oTnipaTaTvetes t 3 g Each of the upper sheets obtained in Examples 7, 8 and 9 and Comparative Example 3 was superposed on the test under sheet, and a pressure of 600 Kg/cm'was applied to develop a color. After allowing the paper to stand for one hour in dark, the spectral absorption curve (fresh) of the developed color in a wavelength region of 700 to 380 my. was measured. The spectral absorption curve of the color after exposure to sunlight for 1 hour and 3 hours, respectively, was also measured. The results are shown in ElG 3, l to (zjIThe light resistance values were calculated in the same way as shown in Comparative Test 1. The results are shown in Table 3.

TA BLE T LIGHT RESISTANCE VALUE OF 3-BENZYL- AMlNO-7-DlETHYLAMINOFLUORAN AT THE ABSORP- TION MAXIMUM AFTER SUNLIGHT EXPOSURE One hour Three hour The fofgbing results showthafihe' fififisistanfi 3-dibenzyl-amino-7-diethylaminofluoran is also increased by using the ether derivativ of the aromatic '7 hydroxyl compound.

On the basis of the spectral absorption curves in FIG. 3, (l) to (4), the movement of the absorption maximum (M) by sunlightexposure is tabulated in Table 4 below:

TABLE 4. MOVEMENT OF THE ABSORPTION MAXIMUM AlOF3-DIBENZYLAMINO-7DIETHYLAMINOFLUORAN BY SUNLIGHT EXPOSURE FOR THE SPECIFIED 'IlME A after A, after one hour three hour sunlight sunlight Fresh A, exposure exposure Imp.) (mu) (mu) Example 7 600 580 560 Example 8.... 600 580 550 Example 9..'. 600 585 550 Comparative Example 3 600 545 485 Examrlsw Eight parts of a 20% sodium'hydroxide solution (as a dispersant) was added to 300 parts of dispersing water, and with stirring, 100 parts of acid clay (Mixusawa Kagaku Kogyo Kabushiki Kaisha) was added gradually. With stirring, a solution of 2 g of hydroquinone dimethyl ether in 30 cc of methanol was gradually added. The stirring was then made slower, and 20 parts (solid content) of styrene butadiene rubber latex (Dow 620; tradename, manufactured by the Dow Chemical Company) was gradually added to form a coating solution. The coating solution was coated on a paper having a unit weight of 40g/m in an amount of lOg/m as solid content, and dried to form an under sheet of pressuresensitive recording paper.

COMPABATIYE EXAMPLE 4 Comparative test 4 I H The upper sheet of Comparative Example 1 was su-.

perpo sed on each of the under sheets obtained in Example l and Comparative Example 4. and a pressure of 600 Kg/cm was applied aaawmpa color. Afifhllowing the paper to stand for 1 hour in dark, the spectral absorption curve (fresh) in a wavelength region of 700 to 380 mp. was measured. The spectral absorption curve of the developedcolor after sunlight exposure for 1 hour and 3 hours, respectively,-was also measured. The results are shown in FIG. 4, (1). The result of Comparative Example 4 was the same as that of Com-j parative Example 1. The light resistance values were calculated in the same way as in Comparative Test 1.

The results are given in Table 5:

TABLE 5.LIGH"F RESISTANCE VALUE OF CRYSTAL VIOLET LACTONE AT THE ABSORPTION MAXIMUM AFTER SUNLIGHT EXPOSURE One hour Three hour The foregoing results indicate that hydroquinone dimethyl ether, in the presenceof the color developer, improved the light resistance of crystal violet lactone. Comparative test 5 The upper sheet [containing microcapsules of 3- methyl-2,2'-spirobi(benzo[flchrornene)1 was superposed enemies the unleashes obtained in Example 10 and Comparative Example 4, and a pressure of 600 Kg/c m w as applied to develop a color. After allowing the paper to stand for 1 hour in a dark place, the spectral absorption curve (fresh) in a wavelength region of 700 to 380 mp. was measured. The spectral absorption curve of the developed color after sunlight exposure for 1 hour and 3 hours, respectively, was also measured.

The results are shown in FIG. 5 (1). The light resistance values were calculated in the same was as in Comparative Test 1. The results are given in Table 6. The result of Comparative Example 4 was the same as that of Comparative Example 2.

TABLE 6.-LIGHT RESISTANCE VALUE OF 3-METHYL- 2,2'-SPIROBI(BENZO{F]CHROMENE) AT THE ABSORP TlON MAXIMUM AFTER SUNLIGHT EXPOSURE One hour Three hour The foregoing results illustrate that hydroquinone dimethyl ether, in the presence of the color developer, improved the light resistance of 3-methyl- 2,2-spirobi- .(lzs zst lsbrsrnsrtasasr svsnts its issslqetip Comparative test 6 The upp er sheet of Comparative Example 3 (containing microcapsules of 3-benzylamino-7-diethylaminofluoran) was superposed on each of the under sheets obtained in Exarmgle 1O a ndComparagtive Example 4, and a pressure of 600 Kg/cm was applied to develop a color. After allowing the paper to stand for I hour in dark, the spectral absorption curve (fresh) in a wavelength region of 700 to 380 mp. was measured. The spectral absorption curve of the developed color after sunlight exposure for 1 hour and 3 hours, respectively, was also measured. The results are shown in FIG. 6, (1) to (2).The'result' of Comparative Example 4 was the same as that of Comparative Example 3. The light resistance values were calculted in the same way as in Comparative Test 1. The results are given in la l .7 z TABLE 7.- LIGHT RESISTANCE VALUE oF 3-DIBENZYL- AMlNO-7-DIETl-IYLAMINOFLUORAN AT THE ABSORP- TION MAXIMUM AFTER SUNLIGHT EXPOSURE One hour Three hour The movement of the absorption maximum A by sunlight exposure, based on FIG. 6,(l) to (2), is shown in Table 8:

TABLE 8. MOVEMENT OF THE ABSORPTION MAXIMUM A1 OF B-DIBENZYLAMlNO-7-DlETHYLAMINOFLUORAN BY SUNLlGl-lT EXPOSURE M after A, after one hour three hour sunlight sunlight Fresh exposure exposure (mu) i -J i Example 600 580 550 Comparative Example 600 545 485 The above results show that hydroquinone dimethyl ether increases the light resistance of 3-dibenzylamino-- 7-diethylaminofluoran and markedly prevents its discoloration.

With other ether derivatives of aromatic hydroxyl compounds, the same results as those obtained in Comparative Tests 1 to 6%re obtainaf Although the present invention has been adequately described in the foregoing specification and examples included therein, it is readily apparent that various changes and modifications may be made without de-' same support or different supports, the improvement? wherein at least one of said layers contains an ether derivative of an aromatic hydroxyl compound which increases the resistance of said color dye reaction product to fadingupon exposure to light, the amount of said ether derivative ranging from 10 to 200% by weight based on the weight of the color former or from 0.2 to 10% by Weight based on the weight of the color developer. 7

2. The pressure-sensitive recording paper of claim 1, wherein said ether derivative is a member selected from the group consisting of p-chloroanisoleppmethylanisole, p-acetoxyanisole, p-acetaminoanisole, o-chloroanisole, m-chloroanisole, Nfi-cyanoethyl p -anisidene, p r netltoxyacetophenone, pmethoxybenzophenone, 2,2-biZEifieih6fifi1'fiy1 1556 pane, catechol dimethyl ether, resorcinol dimethyl ether, hydroquinone dimethyl ether, catechol diethyl ether, resorcinol dipropyl ether, hydroquinone dibutyl ether, p-methoxybenzoic acid ethyl ester, p-ethoxybenzenesdlfonamide, l -phenoxy-2-cyanoethane, 1-phenoxy-2-hydroxyethane, l-phenoxy-Z- chloroethane, diphenyl ether, hydroquinone dibenzyl ether, l,2-dimethoxy-4-(p-methoxyphenoxy) benzene, 1 ,4-dirnethoxy-2-octadecyl benzene, 1-(p-a,cxdimethylbenzylphenoxy)-4-ethoxybenzene, l-ethoxy- 2,3-methylene dioxy benzene, 2,5-dimethoxybenzenesulfonamide, 1,4-dibutyl-2, S-dimethoxybenzene, 1 ,4-diethoxyanthracene, 5 -methyl-1 ,4-diethoxyanthracene, 8-chloro-1,4-diethoxyanthracene, 9,10-dimethoxyanthracene, 4-methyl-9,IO-dimethoxyanthracene, 7-chloro-9 1 O-dimethoxyanthracene, 1- methoxynaphthalene, 2-ethoxynaphthalene, 4-ch1oro- 'l-methoxynaphthalene, S-methyl-lmethoxynaphthalene, 8-chloro-2-ethoxynaphthalene, agd Q-propyl-Z-ethoxynaphthalene.

3. The pressure-sensitive recording paper of iifiiii,"

wherein said color former is a member selected from the group consisting of malachite green, benzoyl leuco methylene blue, crystal violet lactone, Rhodamine B .lactam, 3-dialkylamino Tdialkylamino-fluorans, and

Q -r ne tliyl-Z,2-spirobi(benzo[t]chromene).

4. The pressure-sensitive recording paper of claim 1,

wherein said color developer is a member selected resins. 

2. The pressure-sensitive recording paper of claim 1, wherein said ether derivative is a member selected from the group consisting of p-chloroanisole, p-methylanisole, p-acetoxyanisole, p-acetaminoanisole, o-chloroanisole, m-chloroanisole, N- Beta -cyanoethyl-p-anisidene, p-methoxyacetophenone, p-methoxybenzophenone, 2,2-bi(p-methoxyphenyl) propane, catechol dimethyl ether, resorcinol dimethyl ether, hydroquinone dimethyl ether, catechol diethyl ether, resorcinol dipropyl ether, hydroquinone dibutyl ether, p-methoxybenzoic acid ethyl ester, p-ethoxybenzenesulfonamide, 1-phenoxy-2-cyanoethane, 1-phenoxy-2-hydroxyethane, 1-phenoxy-2-chloroethane, diphenyl ether, hydroquinone dibenzyl ether, 1,2-dimethoxy-4-(p-methoxyphenoxy) benzene, 1,4-dimethoxy-2-octadecyl benzene, 1-(p- Alpha , Alpha -dimethylbenzylphenoxy)-4-ethoxybenzene, 1-ethoxy-2,3-methylene dioxy benzene, 2,5-dimethoxybenzenesulfonamide, 1,4-dibutyl-2, 5-dimethoxybenzene, 1,4-diethoxyanthracene, 5-methyl-1,4-diethoxyanthracene, 8-chloro-1,4-diethoxyanthracene, 9,10-dimethoxyanthracene, 4-methyl-9,10-dimethoxyanthracene, 7-chloro-9,10-dimethoxyanthracene, 1-methoxynaphthalene, 2-ethoxynaphthalene, 4-chloro-1-methoxynaphthalene, 5-METHYL-1-methoxynaphthalene, 8-chloro-2-ethoxynaphthalene, and 6-propyl-2-ethoxynaphthalene.
 3. The pressure-sensitive recording paper of claim 1, wherein said color former is a member selected from the group consisting of malachite green, benzoyl leuco methylene blue, crystal violet lactone, Rhodamine B lactam, 3-dialkylamino-7-dialkylamino-fluorans, and 3-methyl-2,2''-spirobi(benzo(f)chromene).
 4. The pressure-sensitive recording paper of claim 1, wherein said color developer is a member selected from the group consisting of active clay substances and organic acidic substances.
 5. The pressure-sensitive recording paper of claim 4, wherein said active clay substance is a member selected from the group consisting of active clay attapulgite, zeolite and bentonite.
 6. The pressure-sensitive recording paper of claim 4, wherein said organic acidic substance is a member selected from the group consisting of succinic acid, tannic acid, gallic acid, pentachlorophenol, and phenol resins. 